This invention relates in general to ink ribbon cassettes.
Generally, two types of ink ribbon cassettes are known to the art. The one-time carbon ribbons in which each space of the ink ribbon is used only once and multicarbon ribbons in which the ink-delivering layer can be used several times. For example, such a multicarbon ribbon may be used three to six times. In practice, a multicarbon ribbon is transported forward with each print symbol by a fraction of the symbol width, namely, by 1/3 to 1/6. In this case, the ink is removed successively in an overlapping mode.
The advantage of the one-time carbon ribbon is that it permits high print quality, while multicarbon ribbons have long writing duration. On the other hand, one-time carbon ribbons have a short writing life span and multicarbon ribbons often suffer from lower print quality.
An ink ribbon cassette making it possible for one machine to use both a one-time carbon ribbon and a multicarbon ribbon is well known in the art as disclosed in German Patent DE-OS No. 3 106 958. This prior art cassette utilizes a friction gear driven by way of a gear mechanism coupled to the typewriter. In order to make it possible to alter the step-by-step advance for various types of ribbons, exchangeable mating gears are used. The selected elements of the gear mechanism are always used with a particular cassette depending on the type of ribbon used. The speed reduction ratio used for one-time carbon ribbons is accordingly different than that used for multicarbon ribbons.
In a typewriter device disclosed in German Patent DE-GM No. 8 113 006, the transport step for the ribbon can be varied in accordance with the length of a stud placed on the ribbon cassette. Therefore, a one-time carbon ribbon inserted into the typewriter is automatically assigned a larger transport step than a multicarbon ribbon.
These prior art mechanisms have been somewhat satisfactory in allowing the use of different types of ribbons on the same printing device. However, they suffer from the disadvantage that the entire cassette, a cassette part, or a part of the printing apparatus must be changed each time there is a switch from one-time carbon ribbons to multicarbon ribbons.
Accordingly, it is desirable to provide a multicarbon ink ribbon cassette which overcomes the shortcomings of the prior art devices described above and allows easy change from a smaller to a larger multicarbon advance.